The present invention relates to a circuit for generating a position control signal, and more particularly, to a position control signal generating circuit which is operated by a position controller in a programmable logic controller (PLC), a robot or a computer-aided numerical control (CNC) system, and connected to a motor drive.
A typical position control mode of a system is largely divided into a CW/CCW (clockwise/counterclockwise) signal mode and a pulse/sign signal mode. FIG. 1 is a timing diagram showing the CW/CCW signal mode. As shown in FIG. 1, the L shapes of the CW signal and the CCW signal are the same and an object to be controlled, e.g., a motor is driven to rotate in a forward direction according to the CW signal and not the CCW signal. The motor is rotated in the opposite or reverse direction by the CCW signal. FIG. 2 is a timing diagram showing the pulse/sign signal mode. As shown in FIG. 2, a pulse signal is constantly applied to a motor drive and the directions of rotation of the motor are determined by a sign signal.
A conventional position control signal generating circuit is largely divided into the following two circuits.
One is a circuit which generates either the CW/CCW signal or the pulse/sign signal according to a corresponding driver. Such a circuit is advantageous in that it has a simple structure and control method, but it lacks compatibility for a position controller.
The other is a circuit which concurrently generates the CW/CCW signal and the pulse/sign signal and selects a desired signal using an additional selection switch.
FIG. 3 is a block diagram showing a conventional position control signal generating circuit having an additional selection switch.
Referring to FIG. 3, a position controller 1 including a microprocessor unit (MPU) (not shown) and a peripheral circuit (not shown) controls a pulse generator 2 in order to generate a predetermined pulse signal. The pulse signal output from the pulse generator 2 is converted to the CW/CCW signal-and the pulse/sign signal in a CW/CCW circuit 3 and a pulse/sign circuit 4, respectively. Then, a signal for rotation in a forward or reverse direction in the form of a CW/CCW signal is output from a first rotation direction determining unit 5, while a signal for rotation in a forward or reverse direction in the form of a pulse/sign signal is output from a second rotation direction determining unit 6. Next, the output signal of the first or second rotation direction determining unit (5 or 6) is selected by an operator using a selection switch 7 and input to an external drive connector 8. In such a position control signal generating circuit, it is inconvenient for an operator to operate the additional selection switch.
In the meantime, there is a circuit for selecting a desired position control signal using the controller 1 instead of the selection switch 7; however, hardware and software become complicated.